Human topoisomerase I (topo I) is the sole intracellular target of camptothecin (CPT) and other "topo I poisons," some of which are among the most promising anticancer drugs ever identified. Emerald BioStructures, Inc. has successfully completed a Phase I SBIR research program that sought to elucidate the X-ray crystal structure of human topo I in complex with one or another CPT-analogue. We now seek Phase 2 SBIR funds to conduct an integrated structure-based drug design cycle using our 2.0 angstrom structural information of Topotecan bound to the human topo I-DNA covalent complex. We will employ standard computational methods to formulate a three-dimensional quantitative structure-activity relationship (3D-QSAR) model for the camptothecin-type compounds. The 3D-QSAR model will be validated and extended with X-ray crystal structures of additional camptothecin analogues. The Available Chemicals Database and the World Drug Index will be computationally interrogated for ligands that fit into the Topotecan binding pocket of the topo I-DNA binding site. The 3D-QSAR information will be combined with the predicted ligand binding information and chemical intuition to design completely novel camptothecin analogues that have enhanced formulative properties (complete E-ring stability, efficient liposome encapsulation, facile conjugation to polyethylene glycol). The novel camptothecin analogues will be synthesized, purified, and tested for their inhibitory effects on topo I activity, their affinity for the covalent complex using immobilized topo I-DNA covalent complexes, and their cytotoxicity to human tumor cell lines. The most promising compounds will be examined for their efficacy in stopping human tumor growth in the mouse xenotransplant model. PROPOSED COMMERCIAL APPLICATION: Not available